Plastid division control: the PDV proteins regulate DRP5B dynamin activity

Chloroplast division represents a fundamental but complex biological process involving remnants of the ancestral bacterial division machinery and proteins of eukaryotic origin. Moreover, the chloroplast division machinery is divided into stromal and cytosolic sub machineries, which coordinate and control their activities to ensure appropriate division initiation and progression. Dynamin related protein 5B (DRP5B) and plastid division protein 1 and 2 (PDV1 and PDV2) are all plant-derived proteins and represent components of the cytosolic division machinery, where DRP5B is thought to exert constrictional force during division. However, the direct relationship between PDV1, PDV2 and DRP5B, and moreover how DRP5B is regulated during plastid constriction remains unclear. In this study we show that PDV1 and PDV2 can interact with themselves and with each other through their cytosolic domains. We demonstrate that DRP5B interacts with itself and with the cytosolic region of PDV1 and that the two functional isoforms of DRP5B have highly overlapping functions. We further show that DRP5B harbors GTPase activity and moreover that PDV1 and PDV2 inhibits DRP5B-mediated GTP hydrolysis in a ratio dependent manner. Our data suggest that the PDV proteins contribute to the regulation of DRP5B activity thereby enforcing control over the division process during early constriction.